Analyte quantification is an important process in a range of diverse industries. Measurements made on a daily basis in a variety of areas such as pharmaceutical, medical and waste treatment are crucial for maintaining product quality and the well-being of communities. One common method for quantifying an analyte consists in extracting a portion of the analyte and measuring the analyte concentration. However, obtaining a sample for measurement is sometimes difficult. For example, for in vivo measurement of protein in cerebrospinal fluid (CSF) a lumbar puncture (spinal tap) is conducted to obtain a fluid sample. This procedure is not without risk, and as a result is not ideal.
Another method for determining the concentration of an analyte is the absorption measurement, which consists in measuring light after transmission through a sample. However, this method can be complicated by factors such as concentration range and light scattering. The latter process occurs when the direction of light is deviated due to irregular surfaces and/or index of refraction changes within samples. The scattering coefficient μs for a medium represents the average number of scattering events that a photon experiences per unit length of distance traveled. Similarly, the absorption coefficient μa represents the number of absorption events that occur per unit length of distance traveled. Diffuse light scattering complicates measurements since the path length of light is no longer a constant. This leads to an attenuation value that is not directly proportional to analyte absorption. Therefore this method is not suitable for the analysis of liquid samples contained in opaque plastic containers, such as medicine or Nalgene™ bottles. In this situation, the shape and scattering nature of the plastic would make a transmission measurement through the sample difficult.
Therefore there is a need for an improved method of quantification of a component or analyte in a sample which is fast and cost effective.